Even though our ishta devta (the God we believe in and pray to most) may be Shivji and Durga maa, Bāl Krishna is beloved of both Lord Shiv and Durga maa. Child Ram or Krishna is ishta devta of Lord Shiv. Therefore, in Ramcharit Manas, Lord Shiv commences narrating Lord Ram’s story to Maa Parvati by singing a hymn (bhajan) of Lord Ram.
“Mangal bhavan amangal hāri,
Dravahu so Daśarath ajir vihāri.
Bandau bālrup soǐ Rāmu,
Sabsidhi sulabh japat jisu nāmu.”
Hence by offering seva (service) to Bāl Krishna, who is very dear to Lord Shiv also, you gain grace from both.